* {
  margin: 0;
  padding: 0;
}

:root {
  --side-width: 200px;
}

.box {
  display: flex;
}

.left {
  height: 100vh;
  width: var(--side-width);
  background-color: yellow;
}

.right {
  height: 100vh;
  flex: 1;
  background-color: blue;
}

.dialog {
  width: 300px;
  height: 300px;
  background-color: red;
  position: fixed;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  z-index: 999;
}
